Group communications is an area of research which has received a lot of attention recently. This paper focuses on a model
and the architecture of a system which supports group communications by providing group and session management functionality.
This system is an extension of directory services which are used with unicast communications. New functionality is needed
for the dynamics of group communications (members of a connection may change over the lifetime of the connection) and increased
complexity of relations. A model is described which defines six object types which represent the relevant objects. Users and
groups represent real world users and their relations. Sessions and flows describe ongoing group communications. Flow templates
and certificates provide mechanisms for management and security issues. The architecture presented in this paper is transport-independent,
ie it can be used within different group communication platforms. A short sketch of the implementation is given in the last
section.